The objective of present study was to compare and determine the prevalence ofantibiotypes and biotypes of Pseudomonas aeruginosa isolated from patients with burn infection and nosocomial pneumonia in Shiraz, Iran. Thirty isolates from each group of patients were used. Antibiotyping (antibiotic sensitivity profiles) was performed by disk diffusion of Bauer-Kirby method using eleven antibiotics and biotyping (biochemical profiles) was done by standard biochemical procedures. High rate of multi-drug resistant isolates were observed by both groups of patients. P. aeruginosa isolated from burn infection were found more resistant (26.7%) to the all antibiotics used than those from nosocomial pneumonia (6.7%) p < or = 0.04. All P. aeruginosa (100%) isolates from burn infection were resistant to gentamycin, carbenicillin, cephtazidime and cephalothin. The lowest resistance rate was observed with meropenem. Antibiotic susceptibility profiles revealed 11 and 15 different antibiotypes among P. aeruginosa isolates from patients with burn infection and nosocomial pneumonia, respectively. The biochemical profiles consisting of 21 biochemical tests grouped P. aeruginosa into 8 different biotypes. Biotypes BVIII 15(50%) and BIII 11(36.7%) were the most prevalent isolates from burn infection and nosocomial pneumonia, respectively p < or = 0.04. Data obtained in this study revealed that different types of Pseudomonas aeruginosa are involved in burn wound infection and nosocomial pneumonia in this region.